Research On The Dynamic Property And Stability Of The Wind Tower

The cone-shaped tower of the large-scale wind-driven generator has a height of over60meters with the wall thickness of less than1%of the diameter. With the increase in theunit capacity, the tower height and the radius of the impeller, the volatility of the loadresulted from the wind shear, tower-shadow effect and wind fluctuation may feature evermore saliently. By taking into account the dynamics of the tower response and thedeficiency of the structural instability, this paper conducts in-depth research on the towerfrom the perspectives of dynamic performance and stability. The main content andconclusion include the following parts:1. Conducting field measurement of the vibration response of a large-scale windturbine tower at Wuchuan Wind Power Plant. Through the time-domain analysis andfrequency-domain analysis, the inherent frequency, mode of vibration and the dampingratio of the structure are obtained. The comparison of the data measured shows that themaximal vibration acceleration of the tower wall is found at the middle of the tower.2. Analyzing the inherent dynamic property by means of finite element method. In theprocess of modeling, the vane shall be built according to the actual parameter so as toensure the dynamic coupling effect between the vane and the tower. The result shows thatnatural vibration frequency of the wind-driven generator in back-forth and left-rightdirections differs by1.4%. In the further analysis of the influential factors of the inherentfrequency, this paper investigates the specific influence rules of vane stiffness, cabinquality, tower diameter and tower wall thickness on the first-order frequency of thestructure. The resonance analysis finds out that the tower may resonate with the impeller atthe rotation speed of9～11r/min.3. Researching the dynamic response and fatigue life of the structure under thedynamic wind. The wind speed in this paper refers to the superposition of the average windspeed and the pulsation wind speed. The average wind speed model shall be set up in accordance with the wind shear and tower-shadow effect with the pulsation in the windspeed generated by adopting the basis of the harmonic superposition theory. On the basisof the wind speed within the vane swept surface, the impeller stress is calculated with theMomentum-Blade Theory. Meanwhile, it also obtains the loading process of thetransmission of impeller to the tower top in the three directions in space and solves thetower response under three different working conditions, namely, cut-out wind speed,storm condition speed with the unchanged wind direction and the storm condition withwind direction changing by90°. The result demonstrates that the storm condition with theunchanged wind direction is usually accompanied with the minimal tower response. Thedesign of the tower is usually controlled by the displacement values of the tower top underthe working conditions of storm condition with the wind direction changing by90°. At last,the fatigue life of the tower and its cumulative fatigue damage within the designed life arecalculated.4. Conducting stabilized analysis and calculation of the tower by means of eigenvalueand nonlinearity. In the buckling analysis of the eigenvalue, it obtains the first-orderbuckling mode of the tower and the maximal horizontal thrust that the tower could bearbefore buckling under the cabin gravity. Initial disturbance is exerted according to the first-order buckling deformation obtained by means of eigenvalue method for the non-linearsolution of the critical state of buckling and the obtainment of stable bearing capacity ofthe tower and the stress-strain curve of tower after buckling.The research method and conclusion of the dynamic property and stability of the windtower could serve as a reference for the design of the wind tower.